1. FIELD OF THE INVENTION
This invention relates to a method for the production of cellulolytic enzymes by the use of a strain of genus Acremonium cellulolyticus and to a method for the saccharification of cellulosic materials by the use of the enzymes.
2. DESCRIPTION OF THE PRIOR ART
In recent years, the exploitation of reproductive plant biomass as a promising substitute for oil has been receiving earnest consideration. The plant biomass contains cellulosic materials composed preponderantly of cellulose and hemicellulose as principal polysaccharides. Glucose and pentose which are produced by the decomposition of such cellulosic materials are useful as food and feed and as important organic chemicals. Efforts are continued in search of effective methods for the saccharification of cellulosic materials. Particularly, the method for saccharification by the use of hydrolyzing enzymes is arresting keen interest.
Effective hydrolysis of cellulosic materials requires use of numerous enzymes possessing different substrate specificities because the cellulosic materials are composed of various components. Among all these enzymes, cellulase is the most important. The hydrolytic power the cellulase manifests on the cellulosic materials is enhanced when the cellulase is used in combination with a hemicellulase such as xylanase.
Cellulase is the generic term for a group of enzymes which catalyze an enzymatic reaction system for hydrolyzing cellulose into glucose, cellobiose, and cellooligomers. By the mode of activity, the enzymes of this group are divided into C.sub. enzymes (specifically called Avicelase, cellobiohydrolase, FP-ase, and exo-.beta.-glucanase), C.sub.x enzymes (specifically called CMC-ase and endo-.beta.-glucanase), .beta.-glucosidase (otherwise called cellobiase), etc. The cellulase hydrolyzes cellulose eventually into glucose which is the constituent sugar of cellulose because a plurality of such enzymes manifest well-balanced interactions.
Xylanase is one type of hemicellulase. It selectively acts on xylan which is one of the hemicelluloses making up plant cell wall and hydrolyzes the xylan into its constituent monosaccharides such as xylose and xylooligomers which are polymers of xylose.
Trichoderma reesei, Trichoderma viride, and the microorganisms of Aspergillus genus, Penicillium genus, etc. have been widely studied for their ability to produce cellulolytic enzymes but they are not sufficiently productive of such enzymes. The cellulolytic enzymes they produce are deficient in hydrolytic power and thermal stability and, therefore, are incapable of thoroughly hydrolyzing cellulosic materials. The hydrolysates obtained by these cellulolytic enzymes have cellobiose and other oligomers contained therein in large amounts.
The inventors have screened a host of microorganisms occurring widely in nature in search of a cellulolytic enzyme possessing high ability to hydrolyze crystalline cellulose and saccharify the cellulose into glucose. They have found that the cellulolytic enzymes produced by a mold isolated from soil and identified to be Acremonium cellulolyticus (FERM BP-495) include a cellulase which exhibits a strong hydrolytic power to crystalline cellulose and possesses a notably strong .beta.-glucosidase activity and, therefore, enjoys extremely high ability to saccharify cellulose substantially completely into glucose. These cellulolytic enzymes further include a xylanse which excels in thermostability and exhibits high ability to saccharify xylan.
The main object of this invention is to provide a method for the production of cellulolytic enzymes including a cellulase capable of hydrolyzing cellulose substantially completely into glucose and a thermostable xylanase and a method for enhancing the production of the enzymes.